Benzyl-substituted rhodanine derivatives are known to be active in treating inflammation, inflammatory bowel disease (hereinafter IBD), allergies, arthritis, hypoglycemia and muscular dystrophy and in preventing ischemia induced cell damage. For example, U.S. Pat. No. 5,216,002 discloses that certain benzyl-substituted rhodanine derivatives are useful for treating IBD; U.S. Pat. No. 5,158,966 discloses the use of such compounds for treating Type I diabetes; EPO Publication No. 391644 discloses the effectiveness of such compounds for treating inflammation, arthritis and muscular dystrophy, and for preventing ischemia induced cell damage; EPO Publication No. 343643 describes the use of such compounds for treating allergies and inflammation; while EPO Publication No. 587377 discloses these compounds as being effective in treating hypoglycemia.
All of the above patents and publications describe various processes for making the benzyl-substituted rhodanine derivatives disclosed therein. For example, U.S. Pat. No. 5,158,966, herein incorporated by reference, discloses a process for preparing benzyl-substituted rhodanine derivatives comprising reacting 3,5-di-tert-butyl-4-hydroxy benzaldehyde with rhodanine in acetic acid to form 5-{[3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl]methylene-2-thioxo-4-thiazo lidinone, and reducing the resultant 2-thioxo-4-thiazolidinone with hydrogen using palladium on carbon as a catalyst.
Alternately, the alkene of the 2-thioxo-4-thiazolidinone can be reduced by refluxing with diethyl 1,4-dihydro-2,6-dimethyl-3,5-pyridinedicarboxylate, followed by reduction of the thioxo group with hydrogen and palladium on carbon. In another process, reduction of the thioxo group may be accomplished by heating the methyl-2-thioxo-4-thiazolidinone in a mixture of acetic acid in the presence of zinc.
The current processes for preparing benzyl-substituted rhodanine derivatives, as set forth above, have utility. However, these processes require either large amounts of expensive catalyst or generate excessive amounts of environmentally hazardous zinc waste.
The present invention provides an improved process for preparing benzyl-substituted rhodanine derivatives. The process of the present invention can be performed with inexpensive, readily available reagents and eliminates the generation of zinc waste. Other objects, features and advantages of the present invention will become apparent from the subsequent description and the appended claims.